SRAM Cell and Logic Cell Design

ABSTRACT

An embodiment is an integrated circuit structure including a static random access memory (SRAM) cell having a first number of semiconductor fins, the SRAM cell having a first boundary and a second boundary parallel to each other, and a third boundary and a fourth boundary parallel to each other, the SRAM cell having a first cell height as measured from the third boundary to the fourth boundary, and a logic cell having the first number of semiconductor fins and the first cell height.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.16/591,816 filed on Oct. 3, 2019, which is a continuation of U.S.application Ser. No. 16/051,199, filed on Jul. 31, 2018, now U.S. Pat.No. 10,468,418, issued on Nov. 5, 2019, which is a divisional of U.S.patent application Ser. No. 15/170,562, filed on Jun. 1, 2016, now U.S.Pat. No. 10,050,042, issued on Aug. 14, 2018, which claims priority toU.S. Provisional Application No. 62/288,942, filed on Jan. 29, 2016 andentitled “SRAM and Logic Design” which applications are herebyincorporated by reference herein as if reproduced in their entireties.

BACKGROUND

Static random access memory (SRAM) is commonly used in integratedcircuits. SRAM cells have the advantageous feature of holding datawithout a need for refreshing. With the increasing demanding requirementto the speed of integrated circuits, the read speed and write speed ofSRAM cells also become more important.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 and 2 illustrate circuit diagrams of a static random accessmemory (SRAM) cell in accordance with some embodiments.

FIG. 3 illustrates a cross-sectional view of the layers involved in anSRAM cell array and logic cells in accordance with some embodiments.

FIG. 4 illustrates a block diagram of an SRAM array in accordance withsome embodiments.

FIGS. 5A through 5I illustrate an SRAM cell layout in accordance withsome embodiments.

FIG. 6 illustrates a circuit diagram of a logic cell in accordance withsome embodiments.

FIG. 7 illustrates a logic cell layout in accordance with someembodiments.

FIG. 8 illustrates an SRAM cell layout in accordance with someembodiments.

FIG. 9 illustrates a logic cell layout in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

A static random access memory (SRAM) cell, the corresponding SRAM array,and an example logic cell are provided in accordance with variousexemplary embodiments. Some variations of some embodiments arediscussed. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements. Furthermore,although various embodiments are described in a particular context of asix transistor (6T) SRAM cell, other embodiments may also be applied toother SRAM memory cell configurations, such as, eight transistor (8T)SRAM cells, ten transistor (10T) SRAM cells, dual-port SRAM cells, orthe like. Further, the aspects of the disclose embodiments may beapplied to other types of memory cell configurations, such as,magnetoresistive random-access memory (MRAM), dynamic random accessmemory (DRAM), resistive random access memory (RRAM), or the like.Moreover, although various embodiments are described in a particularcontext of an inverter logic cell, other embodiments may also be appliedto other logic cell configurations, such as, NAND gates, NOR gates,multiplexers, latches, flip-flops, or the like.

According to embodiments disclosed herein, SRAM memory cell layouts andlogic cell layouts having synchronized cell designs are presented toshorten the learning cycle for module process development for a newtechnology node. For example, the synchronization of the cell design mayinclude synchronizing the cell heights, synchronizing the patterndesigns for layers, and/or synchronizing the number of fins per cell.This synchronization of the cell designs between memory cells and logiccells shortens the module process development time, makes it easier toleverage technical knowledge between memory and logic cells, and makesit easier to maintain yield during production due to similar designs ofmemory and logic cells.

Referring to FIG. 1, FIG. 1 illustrates a circuit diagram of SRAM cell10 in accordance with some embodiments. SRAM cell 10 includes pull-uptransistors PU-1 and PU-2, which are P-type Metal-Oxide-Semiconductor(PMOS) transistors, and pull-down transistors PD-1 and PD-2 andpass-gate transistors PG-1 and PG-2, which are N-typeMetal-Oxide-Semiconductor (NMOS) transistors. The gates of pass-gatetransistors PG-1 and PG-2 are controlled by a word line (WL) thatdetermines whether SRAM cell 10 is selected or not. A latch formed ofpull-up transistors PU-1 and PU-2 and pull-down transistors PD-1 andPD-2 stores a bit, wherein the complementary values of the bit arestored in storage data (SD) node 110 and SD node 112. The stored bit canbe written into, or read from, SRAM cell 10 through complementary bitlines including bit line (BL) 114 and bit line bar (BLB) 116. SRAM cell10 is powered through a positive power supply node Vdd that has apositive power supply voltage (also denoted as CVdd). SRAM cell 10 isalso connected to power supply voltage Vss (also denoted as CVss), whichmay be an electrical ground. Transistors PU-1 and PD-1 form a firstinverter. Transistors PU-2 and PD-2 form a second inverter. The input ofthe first inverter is connected to transistor PG-1 and the output of thesecond inverter. The output of the first inverter is connected totransistor PG-2 and the input of the second inverter.

The sources of pull-up transistors PU-1 and PU-2 are connected to CVddnode 102 and CVdd node 104, respectively, which are further connected topower supply voltage (and line) Vdd. The sources of pull-downtransistors PD-1 and PD-2 are connected to CVss node 106 and CVss node108, respectively, which are further connected to power supplyvoltage/line Vss. The gates of transistors PU-1 and PD-1 are connectedto the drains of transistors PU-2 and PD-2, which form a connection nodethat is referred to as SD node 110. The gates of transistors PU-2 andPD-2 are connected to the drains of transistors PU-1 and PD-1, whichconnection node is referred to as SD node 112. A source/drain region ofpass-gate transistor PG-1 is connected to bit line BL 114 at a BL node118. A source/drain region of pass-gate transistor PG-2 is connected tobit line BLB 116 at a BLB node 120.

FIG. 2 illustrates an alternative circuit diagram of SRAM cell 10,wherein transistors PU-1 and PD-1 in FIG. 1 are represented as firstinverter Inverter-1, and transistors PU-2 and PD-2 are represented assecond inverter Inverter-2. The output of first inverter Inverter-1(e.g., corresponding to SD node 112) is connected to transistor PG-1 andthe input of the second inverter Inverter-2. The output of secondinverter Inverter-2 (e.g., corresponding to SD node 110) is connected totransistor PG-2 and the input of first inverter Inverter-1. Thus,transistors PU-2/PD-2 and PU-1/PD-1 form a pair of cross-connectedinverters Inverter-1 and Inverter-2.

FIG. 3 illustrates a schematic cross-sectional view of a plurality oflayers involved in SRAM cell 10 and logic cells, which layers are formedon a semiconductor chip or wafer. It is noted that FIG. 3 isschematically illustrated to show various levels of interconnectstructure and transistors, and may not reflect the actualcross-sectional view of SRAM cell 10. The interconnect structureincludes an active region level, a contact level, via levels Via_0level, Via_1 level, Via_2 level, and Via_3 level, and metal-layer levelsM1 level, M2 level, M3 level, and M4 level. Each of the illustratedlevels includes one or more dielectric layers and the conductivefeatures formed therein. The conductive features that are at the samelevel may have top surfaces substantially level to each other, bottomsurfaces substantially level to each other, and may be formedsimultaneously. The contact level may include gate contacts (alsoreferred to as contact plugs) for connecting gate electrodes oftransistors (such as the illustrated exemplary transistors PU-1 andPU-2) to an overlying level such as the Via_0 level, and source/draincontacts (marked as “contact”) for connecting the source/drain regionsof transistors to the overlying level.

Generally, multiple SRAM cells are arranged in a semiconductor die as aSRAM array. FIG. 4 illustrates a block diagram of SRAM array 200according to some embodiments. SRAM array 200 includes a plurality ofmemory cells (SRAM cells 10). In some embodiments, the SRAM array 200 isdivided into multiple SRAM sub-arrays (not shown). In an embodiment,each SRAM cell 10 in SRAM array 200 has a circuit layout as describedabove with respect to FIGS. 1 through 3. Other SRAM circuit layouts maybe used in other embodiments. For example, FIGS. 1 through 3 illustratea six transistor (6T) SRAM circuit layout. Other embodiments may includeSRAM cells 10 having a different number of transistors, such as an eighttransistor (8T) SRAM circuit layout, a ten transistor (10T) SRAM circuitlayout, and various embodiments are not limited to a particular memorycell circuit.

SRAM cells 10 in the SRAM array 200 may be arranged in rows and columns.In an embodiment, the SRAM array 200 may include at least four columnsby 16 rows (denoted as “4×16”) of SRAM cells, such as, 64×64 SRAM cells,128×128 SRAM cells, 256×256 SRAM cells, or the like. In the embodimentwith SRAM sub-arrays, number of SRAM cells in each of the SRAMsub-arrays may be the same or different from the number of SRAM cells inthe other SRAM sub-arrays. However, the number of columns in each of theSRAM sub-arrays is generally the same. Other embodiments may includememory arrays having a different number of memory cells, such as feweror more memory cells.

Generally, SRAM cells 10 in a same column and SRAM array 200 share acommon BL 114 and a BLB 116. For example, each SRAM cell 10 in a samecolumn and SRAM array 200 includes a portion of a BL 114 and BLB 116,which when combined with other SRAM cells 10 in the column and SRAMarray 200 forms continuous conductive lines (the BL and the BLB). BLs114 and BLBs 116 are electrically connected to control circuitry 204,which activates certain BLs 114 and/or BLBs 116 to select a particularcolumn in SRAM array 200 for read and/or write operations. In someembodiments, control circuitry 204 may further include amplifiers toenhance a read and/or write signal. For example, control circuitry 204may include selector circuitry, driver circuitry, sense amplifier (SA)circuitry, combinations thereof, and the like. In some embodiments, thecontrol circuitry 204 includes one or more logic cells that have a samecell height as the SRAM cells 10 in the SRAM array 200, with the cellheight being measured perpendicular to the longitudinal axes of the BL114 and the BLB 116. In the embodiment with multiple SRAM sub-arrays,there may be a different control circuitry 204 for each of the SRAMsub-arrays.

As further illustrated by FIG. 4, SRAM array 200 may further includedummy cells around a periphery of the SRAM cells 10 of the SRAM array200. For example, each row of SRAM array 200 may begin and end with anedge dummy cell 202. The edge dummy cells 202 may have the sameconfiguration and the same size as SRAM cells 10. The edge dummy cells202 may have any suitable configuration and may be included for improveduniformity of fins and/or metal features. As another example, eachcolumn of SRAM array 200 may begin and end with an N-well/P-well strapcell 206. The N-well/P-well strap cells 206 may have any suitableconfiguration and may be included to prevent SRAM cells 10 from directlyabutting against isolation regions (e.g., STI regions) at the activeregion level of the semiconductor die. For example, the N-well/P-wellstrap cells 206 may include dummy gate electrodes and/or dummy finstructures. Gate and/or source/drain contacts may be provided to thedummy gates and/or dummy source/drain regions in N-well/P-well strapcells 206 to provide a dense environment for manufacturing marginimprovement.

FIGS. 5A through 5I illustrate a layout of features of a memory cell(e.g., SRAM cell 10) according to some embodiments. FIGS. 5A through 5Iillustrates features in different levels of SRAM cell 10 (e.g., activeregion level, contact level, via_0 level, M1 level, via-1 level, M2level, see FIG. 3), which are consecutively described for clarity.

Referring first to FIG. 5A, features in the active region level (FIG. 3)and overlying gate electrodes of various transistors in SRAM cell 10 areillustrated. The outer boundaries 10A, 10B, 10C, and 10D of SRAM cell 10are illustrated using dashed lines, which mark a rectangular region. Theactive region level includes a substrate, isolation regions, and wellregions. In some embodiments, an N-well region is in the middle of SRAMcell 10, and two P-well regions are on opposite sides of the N-wellregion. The substrate may be a semiconductor substrate, such as a bulksemiconductor, a semiconductor-on-insulator (SOI) substrate, or thelike, which may be doped (e.g., with a p-type or an n-type dopant) orundoped. The substrate may be a wafer, such as a silicon wafer.Generally, an SOI substrate comprises a layer of a semiconductormaterial formed on an insulator layer. The insulator layer may be, forexample, a buried oxide (BOX) layer, a silicon oxide layer, or the like.The insulator layer is provided on a substrate, typically a silicon orglass substrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the substrate may include silicon; germanium; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs,GaInP, and/or GaInAsP; or combinations thereof.

The well regions may be formed in the substrate. For example, the P-wellregions may be formed in the substrate, and the N-well region may beformed between the P-well regions in the substrate.

The different implant steps for the different wells may be achievedusing a photoresist or other masks (not shown). For example, aphotoresist is formed and patterned to expose the region the substrateto be implanted. The photoresist can be formed by using a spin-ontechnique and can be patterned using acceptable photolithographytechniques. Once the photoresist is patterned, an n-type impurity and/ora p-type impurity implant is performed in the exposed region, and thephotoresist may act as a mask to substantially prevent the impuritiesfrom being implanted into the masked region. The n-type impurities maybe phosphorus, arsenic, or the like implanted in the first region to aconcentration of equal to or less than 10¹⁸ cm⁻³, such as in a rangefrom about 10¹⁷ cm⁻³ to about 10¹⁸ cm⁻³. The p-type impurities may beboron, BF₂, or the like implanted in the first region to a concentrationof equal to or less than 10¹⁸ cm⁻³, such as in a range from about 10¹⁷cm⁻³ to about 10¹⁸ cm⁻³. After the implant, the photoresist is removed,such as by an acceptable ashing process.

After the implants of the well regions, an anneal may be performed toactivate the p-type and/or n-type impurities that were implanted. Insome embodiments, substrate may include epitaxially grown regions thatmay be in situ doped during growth, which may obviate the implantations,although in situ and implantation doping may be used together.

Gate electrode 302A forms pull-up transistor PU-1 with an underlyingactive region 302A in N-well region. In an embodiment, active region302A is fin-based and includes one or more fin structures disposed undergate electrode 304A (e.g., gate electrode 304A may be disposed over andextend along sidewalls of active region 606A). Gate electrode 304Afurther forms pull-down transistor PD-1 with underlying active region302B in a first P-well region (e.g., on a first side of the N-wellregion). In an embodiment, active region 302B is fin-based and includesone or more continuous fin structures disposed under gate electrode 304A(e.g., gate electrode 304A may be disposed over and extend alongsidewalls of active region 302B). Gate electrode 304C forms pass-gatetransistor PG-1 with active region 302B. In an embodiment, gateelectrode 304C is disposed over and extends along sidewalls of activeregion 302B.

As further illustrated by FIG. 5A, gate electrode 304B forms pull-uptransistor PU-2 with an underlying active region 302C in the N-wellregion. In an embodiment, active region 302C is fin-based and includesone or more fin structures disposed under gate electrode 304B (e.g.,gate electrode 304B may be disposed over and extend along sidewalls ofactive region 302C). Gate electrode 304B further forms pull-downtransistor PD-2 with an underlying active region 302D in a second P-wellregion (e.g., on a second side of the N-well region). In an embodiment,active region 302D is fin-based and includes one or more fin structuresdisposed under gate electrode 304B (e.g., gate electrode 304B may bedisposed over and extend along sidewalls of active region 302D). Gateelectrode 304D forms pass-gate transistor PG-2 with underlying activeregion 302D. In an embodiment, gate electrode 304D is disposed over andextends along sidewalls of active region 302D.

In accordance with some embodiments of the present disclosure, pass-gatetransistors PG-1 and PG-2, pull-up transistors PU-1 and PU-2, andpull-down transistors PD-1 and PD-2 are Fin Field-Effect Transistors(FinFETs) as described above where active regions 302A through 302Dinclude one or more fin structures. In accordance with alternativeembodiments of the present disclosure, one or more of the pass-gatetransistors PG-1 and PG-2, pull-up transistors PU-1 and PU-2, andpull-down transistors PD-1 and PD-2 are planar MOS devices having activeregions doped in an upper surface of a semiconductor substrate. FIG. 5Aillustrates a single fin for each active region 302A through 302D inaccordance with some embodiments. In accordance with other embodiments,there may be a single fin, two fins, three fins, or more for each activeregion 302A through 302D, and the number of fins in each active region302A through 302D may be the same or different as other active regionsin SRAM cell 10.

The active regions 302A through 302D are formed in a semiconductorsubstrate. This step may comprise forming shallow trench isolations(STIs) (see FIG. 3) around each active region. The active regions 302Athrough 302D may be doped with the appropriate n-type or p-type dopantsto create n-wells or p-wells for PMOS or NMOS transistors, respectively.Processing may require forming and patterning resist layers in order toform the STIs and the n-wells and p-wells as is known in the art.Alternatively, if FinFETs are to be formed, this step may compriseforming STIs and etching and doping the semiconductor substrate to formthe FinFET active regions 302A through 302D.

In the FinFET embodiments, the fins may be formed in various differentprocesses. In one example, the fins can be formed by etching trenches ina substrate to form semiconductor strips; the trenches can be filledwith a dielectric layer; and the dielectric layer can be recessed suchthat the semiconductor strips protrude from the dielectric layer to formfins. In another example, a dielectric layer can be formed over a topsurface of a substrate; trenches can be etched through the dielectriclayer; homoepitaxial structures can be epitaxially grown in thetrenches; and the dielectric layer can be recessed such that thehomoepitaxial structures protrude from the dielectric layer to formfins. In still another example, heteroepitaxial structures can be usedfor the fins. For example, the semiconductor strips can be recessed, anda material different from the semiconductor strips may be epitaxiallygrown in their place. In an even further example, a dielectric layer canbe formed over a top surface of a substrate; trenches can be etchedthrough the dielectric layer; heteroepitaxial structures can beepitaxially grown in the trenches using a material different from thesubstrate; and the dielectric layer can be recessed such that theheteroepitaxial structures protrude from the dielectric layer to formfins. In some embodiments where homoepitaxial or heteroepitaxialstructures are epitaxially grown, the grown materials may be in situdoped during growth, which may obviate prior and subsequentimplantations although in situ and implantation doping may be usedtogether. Still further, it may be advantageous to epitaxially grow amaterial in an NMOS region different from the material in a PMOS region.In various embodiments, the fins may comprise silicon germanium(SixGe1-x, where x can be between approximately 0 and 100), siliconcarbide, pure or substantially pure germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. For example,the available materials for forming III-V compound semiconductorinclude, but are not limited to, InAs, AlAs, GaAs, InP, GaN, InGaAs,InAlAs, GaSb, AlSb, AlP, GaP, and the like.

The formation of the gates 304A through 304D may include forming adielectric layer, such as silicon dioxide, may be formed over thesemiconductor substrate. The gate dielectric layer (not shown) may beformed by thermal oxidation, chemical vapor deposition (CVD),sputtering, or any other methods known and used in the art for forming agate dielectric. In some embodiments, the gate dielectric layer includesdielectric materials having a high dielectric constant (k value), forexample, greater than 3.9. The gate dielectric materials include siliconnitrides, oxynitrides, metal oxides such as HfO₂, HfZrO_(x), HfSiO_(x),HfTiO_(x), HfAlO_(x), the like, or combinations and multi-layersthereof.

After the formation of the gate dielectric layer, a gate electrode layeris formed over the gate dielectric layer. This gate electrode layer mayinclude a conductive material and may be selected from a groupcomprising polycrystalline-silicon (polysilicon), poly-crystallinesilicon-germanium (poly-SiGe), metallic nitrides, metallic silicides,metallic oxides, and metals. The gate electrode layer may be depositedby physical vapor deposition (PVD), CVD, sputter deposition, or othertechniques known and used in the art for depositing conductivematerials. After deposition, a top surface of the gate electrode layerusually has a non-planar top surface, and may be planarized, forexample, by a chemical mechanical polishing (CMP) process, prior topatterning of the dummy gate electrode layer or gate etch. Ions may ormay not be introduced into the gate electrode layer at this point. Ionsmay be introduced, for example, by ion implantation techniques. Ifpolysilicon is used, in subsequent steps the gate electrode may bereacted with metal to form a silicide to reduce contact resistance. Thegate dielectric layer and the gate electrode layer are then etched suchthat the layers remain on the active regions 302 to form gateelectrodes. Similarly, if FinFETs are used, the gate structures 304 willbe formed over and around the active regions 302. Dielectric spacers maybe formed along the edges of the gate electrodes, and the gateelectrodes may be doped as desired.

After the gates are formed, the source and drain regions for thetransistors may be formed. This may involve doping the active areas oneither side of the gate for each transistor. Different resist layers maybe needed when doping transistors with p-type dopants and when dopingtransistors with n-type dopants.

FIG. 5B illustrates conductive features of SRAM cell 10 in the contactlevel (see FIG. 3) and FIG. 5C illustrates these conductive features inFIG. 5B coupled to the layout of the SRAM cell 10. As shown in FIG. 5B,SD node 110 (see also FIG. 1) includes source/drain contact plug 310Aand gate contact plug 312A, which are the features at the contact levelof SRAM cell 10 (see FIG. 3). Source/drain contact plug 310A iselongated and has a longitudinal direction in the X direction, which isparallel to the extending directions of gate electrodes 304A and 304B.Gate contact plug 312A comprises a portion over, and is electricallyconnected to, gate electrode 304A. In accordance with some embodimentsof the present disclosure, gate contact plug 312A has a longitudinaldirection in the Y direction, with is perpendicular to the X direction.In the manufacturing of the SRAM cell 10 on physical semiconductorwafers, contact plugs 310A and 312A may be formed as a single continuousbutted contact plug.

SD node 112 includes source/drain contact plug 310B and gate contactplug 312B. Gate contact plug 312B has a portion overlapping source/draincontact plug 310B. Since SD node 110 may be symmetric to SD node 112,the details of gate contact plug 312B and source/drain contact plug 310Bmay be similar to gate contact plug 312A and source/drain contact plug310A, respectively, and are not repeated herein for simplicity.

FIG. 5B also illustrates gate contacts 312C and 312D connected to gateelectrodes 304C and 304D, respectively, which may be used toelectrically couple gate electrodes 304C and 304D to one or more WLs asdescribed in greater detail below.

Furthermore, elongated contact plugs 310C and 310D are used to connectto the source regions of pull-down transistors PD-1 and PD-2,respectively, to CVss lines (e.g., electrical ground lines). Elongatedcontact plugs 310C and 310D are parts of the CVss nodes 106 and 108,respectively (see also FIG. 1). Elongated contact plugs 310C and 310Dhave lengthwise directions parallel to the X direction, and may beformed to overlap the corners of SRAM cell 10. Furthermore, elongatedcontact plugs 310C and 310D may further extend into neighboring SRAMcells in a different column that abut SRAM cell 10. Elongated contactplugs 310C and 310D may further be shared between two neighboring SRAMcells in different rows that abut each.

Additionally, contact plugs 310E and 310F are used to connect to thesource regions of pull-up transistors PU-1 and PU-2, respectively toCVdd lines (e.g., supply voltage lines). Contact plugs 310E and 310F areparts of the CVdd nodes 102 and 104, respectively (see also FIG. 1).Contact plugs 310E and 310F may further be shared between twoneighboring SRAM cells in different rows that abut each other.

As further illustrated by FIG. 5B, contact plugs 310G and 310H are usedto connect to the source/drain regions of pass-gate transistors PG-1 andPG-2 to a BL and a BLB, respectively. Contact plugs 310G and 310H areparts of the BL node 118 and BLB node 120, respectively (see also FIG.1). Contact plugs 310G and 310H may further be shared between twoneighboring SRAM cells in different rows that abut each other.

The set of contacts in FIG. 5B may be formed by a damascene or dualdamascene process where a dielectric layer is formed over the SRAM cell10 and etched to form openings that will become contacts to thesubstrate, active regions, or gates. Then, a metal such as copper,aluminum, tungsten, nickel, the like, or a combination thereof may bedeposited into the openings to form the contacts. In some embodiments,the contacts are formed in the same process with the subsequently formedmetallization layer (M1) (see FIG. 5D).

FIG. 5D illustrates features of SRAM cell 10 in the M1 and via_0 levels(see FIG. 3) and FIG. 5E illustrates these conductive features in FIG.5D coupled to the layout of the SRAM cell 10. In FIG. 5D, vias 314(labeled 314A through 314E) are disposed in the via_0 level (see FIG. 3)while conductive lines 316, conductive lines 318, BL 114, CVdd line 324,and BLB line 116 are disposed in the M1 level (see FIG. 3). For example,various conductive lines in the M1 level are disposed over various viasin the via_0 level.

As shown in FIGS. 5D and 5E, vias 314A are connected to gate contacts312C and 312D (e.g., gate contacts for pass-gate transistors PG-1 ofPG-2). Vias 314A are further connected to conductive lines 316, whichmay be used to electrically couple gate electrodes of pass gatetransistors PG-1 and PG2 to one or more WLs as described in greaterdetail with respect to FIGS. 5F and 5G below. Vias 314A and conductivelines 316 may further extend into and shared with neighboring SRAM cellsin a different column that abut SRAM cell 10.

Furthermore, vias 314B are connected to elongated contact plugs 310C and310D (e.g., source contacts of pull-down transistors PD-1 and PD-2).Vias 314B are further connected to conductive lines 318, which may beused to electrically couple sources of pull-down transistors PD-1 andPD2 to CVss lines as described in greater detail with respect to FIGS.5F through 5I below. Furthermore, vias 314B and conductive lines 318 mayfurther extend into neighboring SRAM cells in a different column thatabut SRAM cell 10. Vias 314B and conductive lines 318 may further beshared between two neighboring SRAM cells in different rows that abuteach other.

As further illustrated by FIGS. 5D and 5E, vias 314C and 314D areconnected to contact plugs 310G and 310H, (e.g., source/drain contactsof pass-gate transistors PG-1 and PG-2), respectively. Vias 314C and314D are further connected to a BL 114 and a BLB 116, respectively.Thus, vias 314C and 314D are parts of the BL node 118 and BLB node 120,respectively (see also FIG. 1). Vias 314C and 314D may be shared betweentwo neighboring SRAM cells in different rows that abut each other.Furthermore, as described above, SRAM cells in a same column within theSRAM array 200 share a continuous BL and a continuous BLB. For example,the portion of BL 114 and BLB 116 in the illustrated SRAM cell 10 may beconnected to portions of BL 114 and BLB 116 in other SRAM cells withinthe same column to form a continuous BL and a continuous BLB for eachrow of the SRAM array 200.

Additionally, vias 314E are connected to contact plugs 310E and 310F(e.g., source contacts of pull-up transistors PU-1 and PU-2). Vias 314Eare further connected to a CVdd line 324, which electrically connectssources of pull-up transistors PU-1 and PU-2 to CVdd. Thus, vias 314Eare parts of the CVdd nodes 102 and 104 (see also FIG. 1). Vias 314E mayfurther be shared between two neighboring SRAM cells in different rowsthat abut each other. In an embodiment, a single, continuous CVdd line324 is shared by all SRAM cells in a same column within the SRAM array200. In some embodiments, the CVdd line 324 has a longitudinal directionin the Y direction.

FIG. 5F illustrates features of SRAM cell 10 in the M2 and via_1 levels(see FIG. 3) and FIG. 5G illustrates these conductive features in FIG.5F coupled to the layout of the SRAM cell 10. In FIGS. 5F and 5G, vias326 (labeled 326A and 326B) are disposed in the via_1 level (see FIG. 3)while WLs and CVss pads are disposed in the M2 level (see FIG. 3). Forexample, various conductive lines in the M2 level are disposed overvarious vias in the via_1 level.

As shown in FIGS. 5F and 5G, vias 326A are connected to conductive lines318, which electrically connects source contacts 310C and 310D (e.g.,source contacts for pull-down transistors PD-1 or PD-2) to CVss pads328. These CVss pads 328 will be utilized to electrically connect thesources of the pull-down transistors PD-1 and PD-2 to CVss lines (seeFIGS. 5H and 5I).

Furthermore, vias 326B are connected to conductive lines 316, whichelectrically connects gate contacts 312C and 312D (e.g., gate contactsfor pass-gate transistors PG-1 of PG-2) to a WL. Thus, SRAM cell 10includes WL nodes electrically connected to gates of pass-gatetransistors. In an embodiment, SRAM cells in a same row share a common,continuous WL, which is used to select or deselect SRAM cells in anarray. For example, in order to select a particular SRAM cell, apositive voltage may be applied to a BL/BLB as well as a WLcorresponding to the cell. WL nodes may extend into and be shared withneighboring SRAM cells in a different column that abut SRAM cell 10.

FIG. 5H illustrates features of SRAM cell 10 in the M3 and via_2 levels(see FIG. 3) and FIG. 5I illustrates these conductive features in FIG.5H coupled to the layout of the SRAM cell 10. In FIGS. 5H and 5I, vias332 (are disposed in the via_2 level (see FIG. 3) while CVss lines aredisposed in the M3 level (see FIG. 3). For example, various conductivelines in the M3 level are disposed over various vias in the via_2 level.

As shown in FIGS. 5H and 5I, vias 332 are connected to CVss pads 328,which electrically connects source contacts 310C and 310D (e.g., sourcecontacts for pull-down transistors PD-1 or PD-2) to CVss lines 334.Thus, SRAM cell 10 includes CVss nodes 106 and 108 (see also FIG. 1),which include vias 332. CVss lines nodes 106 and 108 may further extendinto and shared with neighboring SRAM cells in a different column and/orrow that abut SRAM cell 10. In an embodiment, SRAM cells in a same rowshare one or more continuous CVss lines 334. The CVss lines 334 havelongitudinal directions in the Y direction.

Furthermore, as illustrated in FIGS. 5A and 5I, the SRAM cell 10 has afirst cell height. In some embodiments, the first cell height isdetermined by the minimum possible cell height for the SRAM cell 10. Inother embodiments, the first cell height is determined based on theoptimum cell height for logic cells that is then applied to the SRAMcell 10 to synchronize the cell heights of both the SRAM and logic cellson the semiconductor chip.

Additional overlying metal and via layers may be formed on the layout ofFIG. 5I, such as via_2 level, M3 level, via_3 level, and M4 level (seeFIG. 3). These additional metal levels may include additional wordlines, CVss lines, CVdd lines, bit lines, etc. that may be used toprovide additional interconnections between the SRAM cells and/or logiccells.

FIG. 6 illustrates a circuit diagram of a logic cell 400 in accordancewith some embodiments. In this embodiment, the logic cell 400 is aninverter. The inverter cell 400 is powered through a positive powersupply node Vdd that has a positive power supply voltage. The invertercell 400 is also connected to power supply voltage Vss, which may be anelectrical ground. The inverter 400 includes a PMOS transistor P-1 andan NMOS transistor N-1. The gates of the P-1 and N-1 transistors arecoupled together at node 402. The Input of the inverter cell 400 iscoupled to the node 402. The source of the P-1 transistor is coupled tothe Vdd node and the source of the N-1 transistor is coupled to the Vssnode. The drains of the P-1 and N-1 transistors are coupled together atnode 404. The Output of the inverter cell 400 is coupled to the node404.

FIG. 7 illustrates a logic cell layout in accordance with someembodiments. FIG. 7 illustrates features in different levels of theinverter cell 400 (e.g., active region level, contact level, via_0level, see FIG. 3), which are consecutively described for clarity.

Referring first to FIG. 7, features in the active region level (FIG. 3)and overlying gate electrodes of various transistors in inverter cell400 are illustrated. The active region level includes a substrate,isolation regions, and well regions. In some embodiments, an N-wellregion is adjacent a P-well region. The formation and materials of thesubstrate, isolation regions, and well regions are similar to thosedescribed above in reference to FIG. 5A and the descriptions are notrepeated herein.

Gate electrode 504 form transistor N-1 with underlying active regions502A1 and 502A1 in the P-well region. In an embodiment, active regions502A1 and 502A2, are fin-based and include one or more fin structuresdisposed under gate electrode 504 (e.g., gate electrode 504 may bedisposed over and extend along sidewalls of active regions 502A1 and502A2). Gate electrode 504 further forms transistor P-1 with underlyingactive regions 502B1 and 502B2 in the N-well region. In an embodiment,active regions 502B1 and 502B2 are fin-based and include one or morecontinuous fin structures disposed under gate electrode 504 (e.g., gateelectrode 504 may be disposed over and extend along sidewalls of activeregions 502B1 and 502B2). FIG. 7 illustrates a single fin for eachactive region 502A1 through 502B2 in accordance with some embodiments.In accordance with other embodiments, there may be a single fin, twofins, three fins, or more for each active region 502A1 through 502B2,and the number of fins in each active region 502A1 through 502B2 may bethe same or different as other active regions in inverter cell 400. Theformation and materials of the active regions 502 and gate electrode 504are similar to those described above in reference to FIG. 5A and thedescriptions are not repeated herein.

As further shown in FIG. 7, Vss node (see also FIG. 6) includessource/drain contact plug 506A, which is at the contact level ofinverter cell 400 (see FIG. 3). Source/drain contact plug 506A iselongated and has a longitudinal direction in the X direction, which isparallel to the extending directions of gate electrode 504. Source/draincontact plug 506A comprises portions over and electrically connected tosource/drains of active regions 502A1 and 502A2.

Vdd node (see FIG. 6) includes source/drain contact plug 506B. Since Vssnode may be symmetric to Vdd node, the details source/drain contact plug506B may be similar to source/drain contact plug 506A, respectively, andare not repeated herein for simplicity. Source/drain contact plug 506Bcomprises portions over and electrically connected to source/drains ofactive regions 502B1 and 502B2.

Node 404 (see FIG. 6) includes source/drain contact plug 506C, which isat the contact level of inverter cell 400 (see FIG. 3). Source/draincontact plug 506C is elongated and has a longitudinal direction in the Xdirection, which is parallel to the extending directions of gateelectrode 504. Source/drain contact plug 506C comprises portions overand electrically connected to source/drains of active regions 502A1,502A2, 502B1, and 502B2.

FIG. 7 also illustrates a gate contact 512 connected to gate electrode504 which may be used to electrically couple gate electrode 504 to node402 and to one or more conductive features overlying the gate electrodethat can be used to input a signal into the inverter cell 400.

FIG. 7 further illustrates features of inverter cell 400 in the via_0and M1 levels (see FIG. 3). In FIG. 7, vias 508 (labeled 508A through508C) are disposed in the via_0 level (see FIG. 3) while Vss line 510Aand Vdd line 510 d are disposed in the M1 level (see FIG. 3). Forexample, various conductive lines in the M1 level are disposed overvarious vias in the via_0 level.

As shown in FIG. 7, via 508A is connected to source/drain contact 506A(e.g., source/drain contacts for transistor N-1). Via 508A is used toelectrically couple source/drains of transistor N-1 to Vss line 510A.

Via 508B is connected to source/drain contact 506B (e.g., source/draincontacts for transistor P-1). Via 508B is used to electrically couplesource/drains of transistor P-1 to Vdd line 510A.

Via 508C is connected to source/drain contact 506C (e.g., source/draincontacts for transistors P-1 and N-1). Via 508C is used to electricallycouple source/drains of transistors P-1 and N-1 to node 404 and theOutput of the inverter cell 400.

Furthermore, logic cells may be arranged in an array and may share acontinuous Vss 510A and a continuous Vdd 510B. For example, the portionof Vss 510A and Vdd 510B and in the illustrated inverter cell 400 may beconnected to portions of Vss 510A and Vdd 510B in other logic cellswithin the same column or row to form a continuous Vss and a continuousVdd for each row or column of the logic cell array.

Further, as illustrated in FIGS. 5A, 5I, and 7, the SRAM cell 10 and theinverter cell 400 have the same first cell height. In some embodiments,the first cell heights are synchronized by determining by the minimumpossible cell height for the SRAM cell 10 and applying that determinedcell height to the logic cells. In other embodiments, the first cellheight is determined based on the optimum cell height for the invertercell 400 that is then applied to the SRAM cell 10 to synchronize thecell heights of both the SRAM and logic cells on the semiconductor chip.Moreover, in some embodiments, the layouts of SRAM cell and the logiccells are further synchronized to have the same number of active regions(see SRAM cell 10 with four fins and logic cell 400 with four fins).Even further, in some embodiments, the layouts of SRAM cell and thelogic cells are further synchronized to both have elongated source/draincontacts that have a longitudinal directions in the X direction. Thesesynchronizations between SRAM cells and logic cells shortens the moduleprocess development time, makes it easier to leverage technicalknowledge between memory and logic cells, and makes it easier tomaintain yield during production due to similar designs of memory andlogic cells.

FIG. 8 illustrates an SRAM cell 600 layout in accordance with someembodiments. This embodiment is similar to the previous SRAM cell 10embodiment of FIGS. 5A through 5I except that in this embodiment, theSRAM cell 600 includes six total active regions 302 (labeled as 302Athrough 302D2). Details regarding this embodiment that are similar tothose for the previously described embodiment will not be repeatedherein.

The active regions 302A, 302B1, 302B2, 302C, 302D1, and 302D2 may beformed of similar materials and by similar processes as those describedabove and the descriptions are not repeated herein. In this embodiment,the pull-down transistor PD-1 includes two active regions 302B1 and302B2 (e.g. fins 302B1 and 302B2), the pass-gate transistor PG-1includes two active regions 302B1 and 302B2 (e.g. fins 302B1 and 302B2),the pull-down transistor PD-2 includes two active regions 302D1 and302D2 (e.g. fins 302D1 and 302D2), and the pass-gate transistor PG-2includes two active regions 302D1 and 302D2 (e.g. fins 302D1 and 302D2).In some embodiments, the SRAM cell 600 is referred to as ahigh-performance SRAM cell and the SRAM cell 10 is referred to as a highdensity SRAM cell because the SRAM cell 600 has more active regions andcan handle higher current and the SRAM cell 10 is has a smaller cellarea and can be more densely packed onto a chip. Although FIG. 8 onlyshows the conductive features from the active region level through thevia_0 level, the remaining levels (e.g. M1 level through M4 level) (seeFIG. 3) will be subsequently formed as described above in the SRAM cell10 embodiment.

FIG. 9 illustrates a logic cell 700 layout in accordance with someembodiments. This embodiment is similar to the previous logic cell 400embodiment of FIG. 7 except that in this embodiment, the logic cell 700includes up to six total active regions 502 (labeled as 502A1 through502B3). Details regarding this embodiment that are similar to those forthe previously described embodiment will not be repeated herein.

The active regions 502A1, 502A2, 502A3, 502B1, 502B2, and 502B3 may beformed of similar materials and by similar processes as those describedabove and the descriptions are not repeated herein. In this embodiment,the transistor N-1 includes up to three active regions 502A1, 502A2, and502A3 (e.g. fins 502A1, 502A2, and 502A3) and transistor P-1 includes upto three active regions 502B1, 502B2, and 502B3 (e.g. fins 502B1, 502B2,and 502B3).

Furthermore, as illustrated in FIGS. 8 and 9, the SRAM cell 600 hassecond cell height and the logic cell 700 has the second cell height. Insome embodiments, the second cell height is determined by the minimumpossible cell height for the SRAM cell 6000. In other embodiments, thesecond cell height is determined based on the optimum cell height forlogic cells that is then applied to the SRAM cell 60 to synchronize thecell heights of both the SRAM and logic cells on the semiconductor chip.

Moreover, although FIGS. 6, 7, and 9 are described in a particularcontext of an inverter logic cell, other embodiments may also be appliedto other logic cell configurations, such as, NAND gates, NOR gates,multiplexers, latches, flip-flops, or the like.

According to embodiments disclosed herein, SRAM memory cell layouts andlogic cell layouts having synchronized cell designs are presented toshorten the learning cycle for module process development for a newtechnology node. For example, the synchronization of the cell design mayinclude synchronizing the cell heights, synchronizing the patterndesigns for layers, and/or synchronizing the number of fins per cell.This synchronization of the cell designs between memory cells and logiccells shortens the module process development time, makes it easier toleverage technical knowledge between memory and logic cells, and makesit easier to maintain yield during production due to similar designs ofmemory and logic cells.

An embodiment is a semiconductor device including a first static randomaccess memory (SRAM) array including a plurality of SRAM cells, each ofthe plurality of SRAM cells having a first cell height, and a firstlogic cell outside of the first SRAM array, the first logic cell havingthe first cell height.

Another embodiment is an integrated circuit structure including a staticrandom access memory (SRAM) cell having a first number of semiconductorfins, the SRAM cell having a first boundary and a second boundaryparallel to each other, and a third boundary and a fourth boundaryparallel to each other, the SRAM cell having a first cell height asmeasured from the third boundary to the fourth boundary, and a logiccell having the first number of semiconductor fins and the first cellheight.

A further embodiment is a method including forming a first static randomaccess memory (SRAM) array in a first semiconductor device including aplurality of SRAM cells, each of the plurality of SRAM cells having afirst number of semiconductor fins, the SRAM cell having a firstboundary and a second boundary parallel to each other, and a thirdboundary and a fourth boundary parallel to each other, the SRAM cellhaving a first cell height as measured from the third boundary to thefourth boundary, and forming a logic cell in the first semiconductordevice having the first number of semiconductor fins and the first cellheight.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming a semiconductor device, themethod comprising: forming a memory array by forming a plurality ofmemory cells in rows and columns; forming dummy cells along a firstboundary of the memory array and along a second boundary of the memoryarray, the first boundary being parallel to the second boundary; andforming a logic circuit by forming a plurality of logic cells along athird boundary of the memory array, wherein the third boundary isperpendicular to the first boundary, wherein the plurality of memorycells and the plurality of logic cells have a same cell height measuredalong a first direction from the first boundary to the second boundary.2. The method of claim 1, further comprising forming strap cells alongthe third boundary of the memory array and along a fourth boundary ofthe memory array, the fourth boundary being parallel to the thirdboundary.
 3. The method of claim 2, wherein each row of memory cells inthe memory array is formed between a respective first dummy cell at thefirst boundary and a respective second dummy cell at the secondboundary.
 4. The method of claim 3, wherein each column of memory cellsin the memory array is formed between a respective first strap cell atthe third boundary and a respective second strap cell at the fourthboundary.
 5. The method of claim 1, further comprising forming a bitline (BL) and a bit line bar (BLB) over and electrically coupled to eachcolumn of memory cells, wherein the BL and the BLB extend along a seconddirection perpendicular to the first direction.
 6. The method of claim5, wherein the BL and the BLB are formed to be electrically coupled tothe logic circuit.
 7. The method of claim 1, wherein each of theplurality of memory cells is formed to have a first number ofsemiconductor fins, and each of the plurality of the logic cells isformed to have a second number of semiconductor fins, wherein the firstnumber is a same as the second number.
 8. The method of claim 7, whereinthe first number of semiconductor fins and the second number ofsemiconductor fins extend parallel to each other, wherein longitudinalaxes of the first number of semiconductor fins are perpendicular to thefirst direction.
 9. The method of claim 1, wherein each of the pluralityof memory cells comprises: a first pull-up transistor and a secondpull-up transistor; a first pull-down transistor and a second pull-downtransistor that form cross-latched inverters with the first pull-uptransistor and the second pull-up transistor; a first pass-gatetransistor having a first source electrically connected to drains of thefirst pull-up transistor and the first pull-down transistor; and asecond pass-gate transistor having a second source electricallyconnected to drains of the second pull-up transistor and the secondpull-down transistor.
 10. The method of claim 9, wherein gates of thefirst pass-gate transistor and the second pass-gate transistor areelectrically connected to a word line, wherein a first drain of thefirst pass-gate transistor is electrically connected to a bit line (BL),and a second drain of the second pass-gate transistor is electricallyconnected to a bit line bar (BLB).
 11. The method of claim 9, whereineach of the plurality of logic cells comprises: a first transistor,wherein a first source of the first transistor is coupled to a powersupply node; and a second transistor, wherein a second source of thesecond transistor is coupled to a reference voltage node, wherein afirst drain of the first transistor and a second drain of the secondtransistor are connected at a first node, wherein a gate of the firsttransistor and a gate of the second transistor are connected at a secondnode.
 12. The method of claim 11, wherein the first transistor is aP-type transistor, and the second transistor is an N-type transistor.13. A method of forming a semiconductor device, the method comprising:forming a memory cell in a memory region of the semiconductor device,wherein forming the memory cell comprises: forming a first fin in afirst P-well region of the semiconductor device; forming a second fin ina second P-well region of the semiconductor device; forming, in a firstN-well region of the semiconductor device disposed between the firstP-well region and the second P-well region, a third fin and a fourthfin, wherein the first fin, the second fin, the third fin, and thefourth fin extend parallel to each other along a first direction,wherein the memory cell has a first cell height measured along the firstdirection; and forming a logic cell adjacent to the memory cell, whereinforming the logic cell comprises: forming, in a second N-well region ofthe semiconductor device, a fifth fin and a sixth fin; and forming, in athird P-well region of semiconductor device, a seventh fin and an eighthfin, wherein the fifth fin, the sixth fin, the seventh fin, and theeighth fin extend parallel to the first fin, wherein the logic cell hasa second cell height measured along the first direction, the second cellheight being equal to the first cell height.
 14. The method of claim 13,wherein forming the memory cell further comprises: forming a first gateelectrode extending along the first direction; and forming a second gateelectrode extending in parallel to the first gate electrode, wherein ina top view, the first gate electrode overlaps with the first fin, thethird fin, and the fourth fin, and the second gate electrode overlapswith the second fin, the third fin, and the fourth fin.
 15. The methodof claim 14, wherein forming the memory cell further comprises: forminga third gate electrode extending along the first direction; and forminga fourth gate electrode extending along the first direction, wherein inthe top view, the third gate electrode overlaps with the second fin, andthe second gate electrode overlaps with the first fin.
 16. The method ofclaim 14, wherein forming the logic cell further comprises forming athird gate electrode extending along the first direction, wherein in thetop view, the third gate electrode overlaps with the fifth fin, thesixth fin, the seventh fin, and the eighth fin.
 17. A method of forminga semiconductor device, the method comprising: determining a first cellheight for a first design of a static random access memory (SRAM) cell;applying the first cell height of the SRAM cell to a second design of alogic cell such that the first cell height of the SRAM cell is used as asecond cell height of the logic cell; forming the SRAM cell in a memoryregion of the semiconductor device in accordance with the first design;and forming the logic cell in a control circuit region of thesemiconductor device in accordance with the second design, the logiccell formed having a same cell height as the SRAM cell formed.
 18. Themethod of claim 17, further comprising, before forming the SRAM cell andbefore forming the logic cell: determining a first number ofsemiconductor fins for the first design of the SRAM cell; andsynchronizing the second design of the logic cell with the first designof the SRAM cell such that the second design and the first design havethe first number of semiconductor fins.
 19. The method of claim 17,wherein the first cell height is determined based on a minimum cellheight for the SRAM cell.
 20. The method of claim 17, wherein the firstcell height is determined based on an optimum cell height for the SRAMcell.